Vehicle seat suspension component and its method of manufacture

ABSTRACT

A vehicle seat suspension has a thin high strength elastomeric membrane. The membrane is formed from block copolymer material by a process in which a sheet is extruded and tensioned to orient molecules in a select direction with respect to the membrane; the oriented membrane is annealed to retain the orientation during cyclical deformation of the membrane. The sheet form membrane is adapted to be connected with respect to a vehicle seat assembly frame and to serve as a backing for foam seating material and wherein the oriented structure of the membrane provides a two stage modulus in the direction of the orientation for providing static and dynamic load support characteristics which impart passenger comfort without increasing the weight of a seat assembly.

TECHNICAL FIELD

This invention relates to vehicle seat suspensions and their method ofmanufacture and more particularly to vehicle seat assemblies whichutilize an elastomeric component to support a vehicle passenger.

BACKGROUND OF THE INVENTION

Molded foam cushioning elements of the type set forth in U.S. Pat. No.3,161,436, filed Dec. 15, 1964, have been used in automobile andvehicular applications to provide a vehicle seating assembly with bothstatic and dynamic load supporting characteristics for passengercomfort. In such applications the element is supported by a rigidbacking member forming part of the seat assembly frame for attachment tothe vehicle body. In such cases the modulus of elasticity of the foamcushioning element and the thickness of the element is selected toprovide a static deformation which conforms to and comfortably supportsthe weight/shape of different passengers. The cushioning elements have amodulus and are dimensioned to absorb dynamic impacts which aretransferred through the vehicle suspension system into the seatassembly. In such cases the modulus and dimensions of the seatingelement are selected to absorb the impact loading without causing thefoam element to fully compress and bottom out against the rigid backingmember.

Such objectives can only be combined by use of foam elements with athickness that will produce impact load absorption in a material of amodulus that has a comfortable feel under static load conditions. Suchthickness of the foam element increases the weight of the vehicle seatassembly.

U.S. Pat. Nos. 2,251,318 and 4,545,614 disclose vehicle seat assembliesin which elastomeric webbing or strips are stretched between vehicleseat frame components to form a suspension for a seat cover. In the caseof the U.S. Pat. No. 2,251,318 the strips are covered by a layer of foammaterial like spongy material which will impart static comfort to theassembly. The strap components are configured to yield to accommodateimpact loads. The straps are reinforced by fabric to control againstexcessive deflection of natural rubber material of the straps.

The U.S. Pat. No. 4,545,614 uses strips or fibers of a material having amodulus at high deformation which is a multiple of natural rubber tocontrol bottoming out of the suspension system. The use of strips,filaments or straps requires a cover to impart a smooth seating surface.Such covers can set to the shape of the underlying strip array followingperiods of use.

STATEMENT OF THE INVENTION AND ADVANTAGES

A feature of the present invention is to provide an improved seatsuspension for a vehicle seat assembly which has a membrane element ofblock copolymer material oriented to provide a two stage modulus in thedirection of the suspension span for providing a high comfort indexunder static load support conditions and an increasing load supportcharacteristic for absorbing road impacts.

A further feature of the present invention is to provide an improvedmethod for forming an elastomeric membrane for use as vehicle suspensioncomponents wherein a material of block copolymer composition is cast andextruded into sheet form with the material being tensioned duringextrusion to orient the molecular structure of the material; theextruded material is then annealed to fix the material orientation forestablishing a two stage modulus characteristic in the membrane.

Yet another object of the present invention is to provide a seatsuspension means located between a seat cushion and a seat frame forabsorbing vehicular vibrations and providing increased support inresponse to increased load; the seat suspension means including amembrane dimensioned to extend across substantially the full planarextent of the seat frame and including a molecular orientation ofpolymeric material which has a modulus greater across the width of saidmembrane than across the depth thereof.

Still another object of the present invention is to provide a seatsuspension means located between a seat cushion and a seat frame forabsorbing vehicular vibrations and providing increased support inresponse to increased load; the seat suspension means including amembrane dimensioned to extend across substantially the full planarextent of the seat frame and including a molecular orientation ofpolymeric material which is greater across the width of the membranethan across the depth thereof; the direction of orientation beingaligned with the direction in which the membrane is tensioned and theorientation producing a stress to strain relationship which results inincreasing load support in response to increased elongation in thedirection of orientation of the membrane caused by such increased loads.

Another object of the present invention is to provide a new and improvedlow weight, easily assembled vehicle seat having a suspension componentof membrane form which underlies a covering without interrupting smoothsurface features of the covering and which is the sole component tosupport both static and dynamic loads.

Yet another object of the present invention is to provide a seatsuspension component of the type set forth in any of the precedingobjects wherein the component is a sheet form membrane made from a blockcopolymer consisting of polytetramethylene terephthalate polyester andpolytetramethylene ether.

The present invention further resides in various novel constructions andarrangement of process steps and/or parts and further objects, novelcharacteristics and advantages of the present invention will be apparentto those skilled in the art to which it relates and from the followingdetailed description of the illustrated embodiments thereof made withreference to the accompanying drawings forming a part of thisspecification and in which similar reference numerals are employed todesignate corresponding parts throughout the several views, and inwhich:

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle seat seat assembly includingthe present invention;

FIG. 2 is a top elevational view of a seat suspension of the presentinvention;

FIG. 3 is an enlarged fragmentary view of a hook detail;

FIG. 4 is a stress strain curve of a block copolymer membrane used inthe present invention;

FIG. 5 is a chart of a process used in the manufacture of the membraneof the present invention; and

FIG. 6 is a top elevational view of another embodiment of the seatsuspension of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a vehicle seat assembly 10 is illustratedincluding a back frame 12 and a seat frame 14.

The seat frame 14 includes a base tube 16 with side segments 16a, 16bjoined by a front segment 16c. Suspension tubes 18, 20 are provided oneither side of the seat frame 14. Each of the tubes 18,20 include aninwardly and downwardly bent end 22 that is welded to the base tube 16slightly inboard of the side segments 16a, 16b. An aft end 24 on each ofthe tubes 18, 20 is welded to brackets 26, 28, respectively. Thebrackets 26, 28 are located on each side of the rear of the seat frame14. The brackets 26, 28 can be rigidly connected to the back frame 12 orcan serve as a pivot point for a back frame configuration capable ofbeing tilted with respect to the seat frame 14.

The suspension tubes 18, 20 are thereby configured to support a seatsuspension 30 constructed in accordance with the present invention. Thesuspension 30 is representatively shown as a seat in the vehicle seatassembly but is equally suitable for use in the back portion of suchseat assemblies.

The seat suspension 30 is covered with a tin layer 32 of flexible foammaterial or other padding which will provide a comfortable feel when apassenger is seated thereon under static load conditions. It ispreferred that the conformable layer 32 have a modulus that is less thanthe modulus of the seat suspension. The modulus of the conformable layer32, i.e. less than 1 MPa, is also selected to enable it to conform tothe shape of the passenger and transfer such shape to the seatsuspension 30 where the static load is further conformed and supportedin a manner to be discussed.

In the illustrated arrangement the conformable layer 30 also includes acloth trim covering 34. The conformation layer 30 is representativelyshown as including side bolsters 36 (only one illustrated). The backframe 14 supports a cloth covered sculptured foam back 38 which can beof conventional design or modified to include a suspension system suchas seat suspension 30.

The use of the seat suspension 30 of the present invention enables lesspolyurethane foam or other padding material to be used in the vehicleseat assembly 10 and also improves both static and dynamic load supportcomfort of the seat assembly by absorbing high frequency low amplitudevehicular vibrations and also by absorbing large amplitude vehicleexcursions resulting from severe road impacts such as the vehicle wheelshitting pot holes or the like.

In order to produce such desired results, the seat suspension 30includes a sheet form membrane 40 made from a block copolymer ofpolytetramethylene terephthalate polyester and polytetramethylene ether.The material includes a combination of hard crystalline segments of thepolyester and soft amorphous segments of the poly ether. Another exampleof a hard crystalline segment is polyethylene terephthalate polyester.Other amorphous segments can be either polyethyl ether or polypropylether. Annealing the material at a specific temperature while they areunder tension orients the polyester molecules in one direction whileleaving the poly ether molecules unaffected. As will be morespecifically described, such orientation can produce a two stage stressto strain curve in which the curve has a relatively flat slope for afirst range of seat suspension deflections and a relatively higher slopefor a second range of seat suspension deflections.

One aspect of the present invention is to provide a process for making asheet form membrane 40 with molecules oriented therein to producedesired stress strain characteristics. As shown in FIG. 5, the processincludes the steps of preparing a mass of block copolymer material ofthe type specified above and maintaining it in a homogeneous state at atemperature of 260° C. by suitable mixing and heater means.

The blended material is directed into an extruder with a suitable die toproduce a sheet. The sheet is drawn from the extruder by calenderingrollers adjusted to speeds which maintain the sheet under tension in thedirection of extrusion to produce a first axial orientation of thesheet. If desired, the sheet can be engaged by a tenter to increase thewidth of the sheet and maintain transverse tension thereon to producebiaxial orientation of the sheet.

The extrusion is then heated to anneal the material under tension. Thebiaxial orientation of the polyester molecules produces a membranehaving the stress strain curve shown in FIG. 4.

The resultant membrane 40 is a strong and durable material especiallysuited for seat suspension applications. The seat suspension 30 equippedwith the membrane 40 produces a well cushioned and comfortable ridewhile offering increased load support under impact conditions of theaforediscussed type. The stress strain curve 42 of the membrane 40 in adirection along the axis X--X is shown in FIG. 4. It shows that themembrane has high strength in the range of 75-280 MPa as compared tonatural rubber elastomer membranes with a strength in the range of 10-20MPa.

Further, the curve 42 at low strains has a relatively low slope portion44. Hence, a small change is static load or small amplitude vibrationswill produce a large change in elongation of the membrane 40 along theaxis X--X between the portions thereof which are connected to the seatframe 14. In this range of elongation the membrane and the layer of foamthereon will feel comfortable because they easily conform to the shapeof the passenger.

The curve at high strains has a very high slope portion 46 and hence themembrane will stiffen when large loads are imposed thereon by severeroad impacts or the like. In such cases the seat suspension 30 willstiffen and provide excellent support without bottoming out onunderlying frame components of a seat assembly.

In the illustrated embodiment of FIGS. 1-3 the side edges 48, 50 of themembrane 40 are wrapped around and heat sealed to spaced parallel metalrods 52, 54, respectively. Hooks 56 are connected to each of the rods52, 54 at spaced locations therealong. The hooks 56 are attached to thesuspension tubes 18, 20 to suspend the membrane 40 therebetween to beprestretched into a range of 10%-25% elongation to provide a desiredinitial load support capability.

Orientation of the membrane 40 along the axis X--X increases the modulusand the tensile strength of the membrane 40 only in the direction oforientation as seen in the case of the following Table I. The amount ofincrease in tensile properties is proportional to the degree oforientation.

                                      TABLE I                                     __________________________________________________________________________    Tensile Properties of Oriented Hytrel Membranes and Filament                                            Modulus at                                                                           Tensile                                                          Thickness                                                                           100% Elong.                                                                          Strength                                                                           Ultimate                                Sample                                                                             Orientation                                                                         Comment  Mil(mm)                                                                             (MPa)  (MPa)                                                                              Elongation %                            __________________________________________________________________________    Original   No orientation                                                                         40(1.57)                                                                            10.3    55.7                                                                              1111                                    S.sub.1                                                                            2.25 X                                                                              Oriented in X                                                                          11(0.43)                                                                            11.4    53.0                                                                              1328                                               direction                                                                     Tensile in Y                                                                  direction                                                          S.sub.2                                                                            2.25 X                                                                              Oriented in X                                                                          14(0.58)                                                                            50.5   107.9                                                                              220                                                direction                                                                     Tensile in X                                                                  direction                                                          D.sub.1                                                                            2.5 X Oriented in                                                                            4.3(0.17)                                                                           29.1   102.5                                                                              333                                          3 Y   X & Y directions                                                              Tensile in                                                                    X direction                                                        D.sub.2                                                                            4.4 X Oriented in                                                                            3.7(0.14)                                                                           66.8   130.9                                                                              195                                          3 Y   X & Y directions                                                              Tensile in Y                                                                  direction                                                          Filament   Oriented in                                                                            --    --     185.0                                                                              110                                                X direction                                                                   Tensile in                                                                    X direction                                                        __________________________________________________________________________

In the embodiment of the invention shown in FIG. 6, holes 60 areintroduced into a membrane 62 to provide for breathability and toprovide means for adjusting the modulus of a seat suspension 64. In theillustrated embodiment the membrane 62 is oriented in the same manner asmembrane 40. The holes 60 are placed in the center region of themembrane 62 without affecting the strength of the membrane in theunoriented direction perpendicular to axis X--X. Consequently, ifdesired the process defined above can provide an alternative step ofprepunching the membrane as it leaves the extruder and prior to beingtensioned and annealed.

The results of the addition of holes in a sample segment of a membraneis set forth in following Table II.

                  TABLE II                                                        ______________________________________                                        Tensile Strength and elongation of Hytrel Membranes                           Oriented in the X-Direction. Some of the samples had                          3 mm holes punched in the center of the 6.35 gauge width.                     Direction             Tensile  Ultimate                                       of Tensile                                                                              Hole        Strength Elongation                                     Pull      Present?    (MPa)    (%)                                            ______________________________________                                        X         No          75       180                                            X         Yes         67       100                                            Y         No          23       925                                            Y         Yes         38       858                                            ______________________________________                                    

From the foregoing, it should be apparent that the present inventionprovides a novel seat assembly of light weight and with improved staticand dynamic comfort of the seat because of a full uninterrupted surfacesupport of the passenger by means which will accommodate and conform tothe shape of a passenger and which will increase in strength to supportadditional dynamic impact loads without bottoming out.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the invention may be practiced otherwise than asspecifically described herein and yet remain within the scope of theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a vehicle seatassembly having a seat frame with a seat thereon and a back assemblyextending generally vertically with respect to the seat frame theimprovement comprising:a seat suspension means located between the seatand the frame and suspended from the frame for absorbing vehicularvibrations and providing increased support in response to increasedload; said seat suspension means including a membrane dimensioned toextend across substantially the full planar extent of the frame andincluding a direction of orientation of polymeric material which isgreater across one dimension of said membrane so that the membrane has agreater modulus of elasticity in the direction of orientation and alesser modulus of elasticity in other directions.
 2. In the combinationof claim 1, said direction of orientation being aligned with thedirection in which increased loads impose tension on said membrane andsaid orientation producing a stress to strain relationship which resultsin increasing load support in response to increased elongation in thedirection of orientation of the membrane caused by such increased loads.3. In the combination of claim 1, said membrane being made from a blockcopolymer having a hard crystalline segment and a soft amorphoussegment.
 4. In the combination of claim 3, said copolymer consisting ofpolytetramethylene polyethylene terephthalate polyester andpolytetramethylene ether and having a modulus of elasticity in thedirection of molecular orientation which provides a low slope stressstrain curve segment so as to produce large changes in elongation inresponse to small load changes attendant to shaping the seat to theshape of a passenger and which orientation further provides a higherslope stress strain curve segment to stiffen said membrane underincreased loads to provide increased load support during extremevehicular excursions.
 5. In the combination of claim 1, said membranehaving reinforcing means thereon and means for connecting saidreinforcing means to the seat frame to align said reinforcing meansbetween the seat frame and said membrane in the direction of orientationof said membrane.
 6. In the combination of claim 5, said reinforcingmeans including reinforcing rods and heat sealed edges on said membraneformed around said rods to hold said rods with respect to saidmembrane;said connector means including hook means joined respectivelyto said reinforcing rods and the seat frame.
 7. In the combination ofclaim 1, said membrane having a layer of foam material located injuxtaposed covering relationship therewith, said foam having a modulusof elasticity in the range of less than 1 MPa which combines with thenonzero modulus of elasticity of said membrane to conform to the shapeof a passenger and to shape said membrane to cause it to further supportsuch shape.
 8. In the combination of claim 7, said direction oforientation being aligned with the direction in which increased loadsimpose tension on said membrane and said orientation producing a stressto strain relationship which results in increasing load support inresponse to increased elongation in the direction of orientation of themembrane caused by such increased loads.
 9. In the combination of claim7, said membrane being made from a block copolymer having a hardcrystalline segment and a soft amorphous segment.
 10. In the combinationof claim 7, said block copolymer consisting of polytetramethyleneterephthalate polyester and polytetramethylene ether and having amodulus of elasticity in the direction of molecular orientation whichprovides a low slope stress strain curve segment so as to produce largechanges in elongation in response to small load changes attendant toshaping the seat to the shape of a passenger and which orientationfurther provides a higher slope stress strain curve segment to stiffensaid membrane under increased loads to provide increased load supportduring extreme vehicular excursions.
 11. In the combination of claim 7,said membrane having reinforcing means thereon and means for connectingsaid reinforcing means to the seat frame to align said reinforcing meansbetween the seat frame and said membrane in the direction of orientationof said membrane.
 12. In the combination of claim 11, said reinforcingmeans including reinforcing rods and heat sealed edges on said membraneformed around said rods to hold said rods with respect to saidmembrane;said connector means including hook means joined respectivelyto said reinforcing rods and the seat frame.
 13. In a vehicle seatsuspension including an interface between a frame of a vehicle seatassembly and a layer of foam material for defining a support foraccommodating the shape of a passenger at a first modulus of elasticityand for supporting road impact imposed loads at a second modulus ofelasticity greater than the first modulus of elasticity the improvementcomprising:an extruded sheet of elastomeric material having a firstmodulus of elasticity in a first range of elongation of the elastomericmaterial and a second modulus of elasticity greater than the firstmodulus in a second range of elongation which is greater than the firstrange of elongation; means for connecting the extruded sheet withrespect to the frame to place it in tension to prestretch it to thelower limit of the first range of elongation; said first range ofelongation accommodating displacements of the layer of foam materialimposed thereon by static loads placed on the foam material imposedthereon by static loads placed on the form layer while conforming theshape of said extruded sheet to such displacements and said second rangeof elongation stiffening the extruded sheet to support road impactloading while restricting further elongation of said extruded sheet tothe confines of the seat frame to which said extruded sheet is attached.